CFU - Colony Forming Units

CFU (Colony Forming Units) is a term from microbiology that indicates the amount of living microorganisms in a liquid. This number, determined by counting individual colonies, describes the number of organism cells in water that are able to multiply. The organisms are bacteria or fungi living and multiplying in water. Colony forming units are important in microbiology to observe cell culture development and to determine microorganism quantities in drinking water or river water.

For CFU measurement, a period of time must be considered since a single bacterium can quickly become an entire colony. This helps determine how quickly bacteria develop and what danger the water poses when consumed. To ensure comparability between different analyses, CFU results are always referred to as colony forming units per 100 ml.

The standard of keeping bacteria in water at less than 100 CFU/ml in drinking water was introduced following an 1892 cholera outbreak in Hamburg, Germany, investigated by Robert Koch. This standard remains used worldwide today.

Bacteria or fungi in drinking water can endanger consumer health, so drinking water is strictly monitored through regulations at national or European levels, with corresponding limit values described for each water type. In the United States, this is regulated by the EPA (Environmental Protection Agency). The World Health Organization recommends the same limit values for CFU in its drinking water safety recommendations.

Water samples are placed in petri dishes and kept at defined temperatures, allowing microbes to breed. Colonies are counted manually by certified laboratories, typically under magnification. Results are expressed in CFU/ml. For drinking water, the upper limit is 100 CFU/100 ml; cooling water should not exceed 10,000 CFU/100 ml.